Janet Kwasniak's blog on consciousness and the brain

What meets where

A paper looking at the newly re-found nerve bundle, the vertical occipital fasciculus, connects it with “The Man who Mistook his Wife for a Hat”. Why would someone reach for an object in a different place than the object was? ScienceDaily has a report (here), “Scientists chart a lost highway in the brain”.

The ‘what’ and ‘where’ visual pathways have been studied for some time, but there appeared to be little connecting them until they had passed out of the early visual area. A nerve tract that was known over a hundred years ago and was lost to the anatomy texts until recently, connects the ‘what’ and ‘where’ maps. “Our new study shows that the VOF may provide the fundamental white matter connection between two parts of the visual system: that which identifies objects, words and faces and that which orients us in space. … The structure forms a ‘highway’ between the lower, ventral part of the visual system, which processes the properties of faces, words and objects, and the upper, dorsal parietal regions, which orients attention to an object’s spatial location.“

This long flat nerve tract was described long ago and then mysteriously disappeared from view. Why? “The answer may be scientific rivalry. In their earlier paper, Pestilli and collaborators attributed the VOF’s disappearance to competing beliefs among 19th-century neuroanatomists. In contrast to Wernicke, Theodor Meynert, another prominent scientist in Germany, never accepted the new structure due to his belief that all white matter pathways ran horizontally. Over time, the VOF faded into obscurity.”

Are other structures being overlooked because they are up and down rather than side to side or back to front, or in some other way are counter to orthodoxy?

Here is the abstract (H. Takemura, A. Rokem, J. Winawer, J. D. Yeatman, B. A. Wandell, F. Pestilli. A Major Human White Matter Pathway Between Dorsal and Ventral Visual Cortex. Cerebral Cortex, 2015; DOI: 10.1093/cercor/bhv064): “Human visual cortex comprises many visual field maps organized into clusters. A standard organization separates visual maps into 2 distinct clusters within ventral and dorsal cortex. We combined fMRI, diffusion MRI, and fiber tractography to identify a major white matter pathway, the vertical occipital fasciculus (VOF), connecting maps within the dorsal and ventral visual cortex. We use a model-based method to assess the statistical evidence supporting several aspects of the VOF wiring pattern. There is strong evidence supporting the hypothesis that dorsal and ventral visual maps communicate through the VOF. The cortical projection zones of the VOF suggest that human ventral (hV4/VO-1) and dorsal (V3A/B) maps exchange substantial information. The VOF appears to be crucial for transmitting signals between regions that encode object properties including form, identity, and color and regions that map spatial information.”